1. Technical Field
The present disclosure relates to a power circuit, a control method, a power system, and a package structure of a power circuit. More particularly, the present disclosure relates to a power circuit, a power system, and a package structure of a power circuit which have a quasi-cascade structure.
2. Description of Related Art
High efficiency and high power density are always the industry's requirements for the power conversion devices. High efficiency means the reduction of the power consumption, and it efficiently uses the energy to facilitate the energy saving, carbon reduction, and the environment protection. High power density means small size, light weight, reduced space requirements, and thereby it further reduces the costs.
As one of the important components of the switch-mode power supply, the characteristics of the active power component play a very critical rule to the performance of the power source. With the succeeding progress of the semiconductor industry, and since the properties of the Si materials active power component have been close to the theoretical limit, the power characteristics thereby are elevated to a very high level. The active power components use wide bandgap materials, such as Silicon Carbide (SiC) and Gallium Nitride (GaN), are receiving more attention because an opportunity to have smaller internal impedances, smaller switching losses, and higher operating temperatures which promote the efficiency and power density.
Usually SiC components and GaN components include two types: the normally-on type (that is, when the gate voltage=0, the component is on; when the gate voltage <0, the component is off) and the normally-off type (that is, when the gate voltage=0, the component is off; when the gate voltage >0, the component is on). However, an obvious problem of the normally-on type components is how to resolve the starting problem.
As shown in FIG. 1A, a switch component of a buck circuit 10 is a normally-on switch. For example, when the normally-on switch (e.g., the transistor Q1 and the transistor Q2) is on when the gate voltage=0, and the normally-on switch is off when the gate voltage is negative. Because the gate voltage of the transistor Q1 and that of the transistor Q2 are 0 voltage during an initial state of the circuit (that is, when the circuit is not yet connected to a power source; the input power supply Vin=0), the transistor Q1 and the transistor Q2 are at the on state. When the circuit is powered, that is, when the input power source Vin is not equal to 0 voltage; the transistor Q1 and the transistor Q2 will be damaged.
As shown in FIG. 1B, that is, a normally-off switch (e.g., the transistor Qin) is coupled to an input power source Vin of the buck circuit 11. Before the circuit is powered, a gate voltage of the transistor Qin is 0 voltage, the transistor Qin is at an off state. When the input power source Vin is on, the normally-off switch Qin is responsible for blocking, to thereby ensure the circuit safety. Once a control signal of the normally-on switch starts to function normally, the transistor Qin constantly is turned on, and thus a safe enabling is achieved. However, the imperfection is that, a voltage stress of the transistor Qin is the same as that of the transistor Q1 and that of the transistor Q2, and are all equal to the input power source Vin. In addition, usually the transistor Qin is a Silicon Metal-Oxide-Semiconductor (Si MOS) transistor, and in situations where the voltage level equals to the that of the GaN power components, the loss caused by the on-resistance of the transistor Qin may not be ignored, therefore it is difficult to achieve popular usage.
As shown in FIG. 1C, the buck circuit 12 is with a cascade structure, which is more commonly used in the applications of the GaN components, especially in a state that the voltage is higher, such as 600 volt. A structure constructed by high voltage components and low voltage components connected in series may have better control properties, which is alike to the normally-off Si components.
However, since the GaN components and the Si components both operate under a high frequency, the control loss is the sum of the GaN components and Si components, that is, the control loss is increased. Furthermore, the Si components are added in the form of series connection and work under a high frequency, and thus directly lead to the increase of distributed inductance so that it results in more electromagnetic interferences. Moreover, the GaN components decide the shutdown control according to the shutdown current, hence the larger the shutdown current, the faster the shutdown control; oppositely, the smaller the shutdown current, the slower the shutdown control, therefore making the GaN components is unable to perform at its optimal characteristics. Besides, the GaN components themselves have no reverse recovery, but the diode connecting in series with the Si components has severe reverse recovery, thus it eliminated the advantage of the GaN components and makes the GaN components not suitable for the situation of large reverse recovery.
In summary, it is indeed an important issue in this technical field that how to improve the ability of the GaN components to resolve the problems of the increasing of the control loss, the loop inductance, the reverse recovery, and the restricted characteristics of the GaN components, to therefore promote the power density or the conversion efficiency of the power conversion device.